Toothbrush

ABSTRACT

A toothbrush made partly of a hard plastic material and partly of an elastomeric material, characterized in that at least part of the elastomeric material comprises an inner core ( 23 ) of a first soft elastomeric material wholly or partly enclosed within an outer flexible skin ( 24 ) of a second polymer material having different physical characteristics to the inner core polymer. Processes for making such a toothbrush are also described.

This invention relates to toothbrushes, in particular to toothbrushesmade of two construction materials being a hard plastic and a softerelastomeric material.

Such toothbrushes are known. For example EP 0 336 641 A discloses atoothbrush having elastomeric material grip-enhancing pads on itshandle. WO 92/17092 discloses a toothbrush having elastomeric materialparts forming a flexible link between its head and its handle. WO92/017093 discloses a toothbrush having elastomeric material parts inits head, thereby modifying the flexibility at its head. DE 3923495 Adiscloses a toothbrush having elastomeric material inserts in cut-outsbetween the handle and neck region, also to modify flexibility. EP0310482 discloses a toothbrush having elastomeric material parts aroundits head as a soft buffer to absorb impact forces between the head andthe mouth of the user. EP 0371293 A discloses a toothbrush havingelastomeric material parts in its neck. WO 94/05183 discloses atoothbrush having elastomeric material parts in one, two or three placesin its handle, neck and head. Other parts of the head, handle and neckregion of the above-mentioned toothbrushes are made of hard plasticmaterials. The above-mentioned disclosures are only examples of many inthe literature. Two component toothbrushes of this type have been madeand sold commercially for many years, for example the applicant's DrBEST™ and AQUAFRESH ™ range of toothbrushes.

The above-mentioned two component toothbrushes are made by a process ofinjection moulding in which the hard plastic parts are first injectionmoulded to form a frame or skeleton having cavities which define theposition, size and shape of the elastomeric material parts to be formedtherein, and in which cavities the elastomeric material parts aresubsequently formed by a second injection moulding of fluid elastomericmaterial. Such a process is described for example in WO 94/05183.

A problem with known two-component toothbrushes of this type is that theelastomeric materials which are used need to be relatively soft, forexample to enable them to fulfil their function of forming soft griphandles, flexible links or soft buffers. Soft elastomeric materials arerelatively vulnerable to physical damage during use, e.g. due to impactwith and abrasion from tooth surfaces or other surfaces. Softelastomeric material s tend to be absorbent, and consequently when suchtoothbrushes are used, especially when they are exposed to detergents,soaps or toothpastes, moisture and dirt etc, their elastomeric materialparts can absorb these substances. As a consequence these elastomericmaterial parts can deteriorate, become discoloured or dirty, and suchabsorbed substances can be difficult to remove by cleaning.

It is an object of this invention to offer a solution to this problem.

According to this invention a toothbrush is provided comprising ahandle, a head on which are mounted bristles, with optionally a neckregion between the head and handle, the toothbrush being made partly ofa hard plastic material and having at least one part made of anelastomeric material, characterised in that at least part of the atleast one elastomeric material part comprises an inner core of a softelastomeric material wholly or partly enclosed within an outer flexibleskin of a polymer material having different physical characteristics tothe inner core material.

The term “elastomeric” material as used herein includes natural andsynthetic elastomeric materials which have a semi-rigid rubbery nature,i.e. being soft and resilient to the touch, deforming under handpressure and springing, preferably rapidly, back to substantially orexactly its original shape on release of the hand pressure. The termalso includes polymers which are not inherently of a rubbery nature butwhich are rendered rubbery in nature by for example foaming or othertreatment.

By “soft” herein is meant deforming under the pressure of the hand,particularly under pressures applied during normal use of the toothbrushin brushing the users teeth.

The outer skin should be a flexible skin, so that the elastomeric corematerial can deform as pressure is applied to the outer skin andtransmitted to the core elastomeric material via the skin. It isdesirable that the outer polymer skin binds with, preferably has goodbonding characteristics to, the hard plastic material of the toothbrush.

The physical characteristics of the inner core and the skin polymer maydiffer in various ways. The skin may be a polymer material which isharder than the soft core elastomeric material. Additionally oralternatively the skin material may be a polymer material which is moreresistant to physical damage or penetration by absorption of substancesthan the core elastomeric material as mentioned above. Additionally oralternatively the skin polymer material may have better surfaceproperties than the core elastomeric material, e.g. having bettertactile properties or being more easy to print upon than the coreelastomeric material. Additionally or alternatively the core and skinmay differ in quality, e.g. the inner core elastomeric material being arelatively cheap, low quality recycled elastomeric material and theouter skin material may be a higher quality, e.g. non-recycled polymer.For example there may be an inner core of a less dense, or soft oreasily damaged or absorbent elastomeric material and an outer skin of amaterial which is denser or relatively less soft or more resistant todamage or less absorbent. The inner core elastomeric material may be acheap elastomeric material, e.g. a recycled low quality e.g. easilydamaged, elastomeric material, and the outer skin may be a thin skin ofan expensive polymer of high quality or having desirable surfaceproperties high quality. In this way the superior surface properties ofthe more expensive polymer may be enjoyed whilst minimising the quantityused.

By means of the invention the elastomeric material parts of thetoothbrush may benefit from the softness of the core elastomericmaterial, e.g. in providing a comfortable grip, in forming a flexibleregion in the toothbrush, or in providing a soft buffer around the head,whilst the outer skin can provide a coating having advantageousproperties, e.g. of physical resistance, resistance to absorption ofsubstances, hand-feel, or of printing onto its surface. The outer skincan enhance the bonding of the elastomeric material and hard plasticparts of the toothbrush as this bonding can be made between the outerskin and the hard plastic parts, and a polymer material may be selectedfor the outer skin which has better bonding characteristics with thehard plastic material than the core elastomeric material.

In the toothbrush of this invention the elastomeric material part(s) maybe in any or all of the parts where elastomeric material is at presentused in two-component toothbrushes of the state of the art. For examplethe elastomeric material part(s) may comprise a pad on the grip handle,a flexibility modifying region, for example in the handle, neck or heador between the handle and neck or the neck and the head, or a softbuffer around the head. The elastomeric material part is preferably apad on the grip handle. The toothbrush of the invention may alsoincorporate parts which are made of conventional elastomeric material,i.e. of soft elastomeric material throughout without the less softcoating skin.

The outer skin and inner core elastomeric material polymers shouldpreferably be compatible to encourage bonding between them. The outerskin and inner core materials may be inherently compatible, oralternatively they may be of materials which are modified to becompatible with each other.

The outer skin polymer may be an elastomeric or non elastomericmaterial.

For example the inner core material and the skin material may comprisethe same polymer, i.e. including the same monomeric units, but includingdifferent additives or quantities of additives to give the core and skinmaterials such different physical characteristics.

For example the core and outer skin may comprise the same polymer, i.e.both being an elastomeric material and comprising the same monomerunits, but being different grades of the same polymer. For example suchdifferent grades may differ in their relative density, softness,resistance to damage or ability to absorb environmental substances orother characteristics.

The core and outer skin may be different polymers, i.e. comprisingdifferent monomer units or different combinations of monomer units.

In a preferred embodiment the core comprises a foamed elastomericmaterial. With such a core the outer skin may be an elastomeric materialor a non-elastomeric material. If the skin in this embodiment is anelastomeric material it may be the same elastomeric material as the corebut in a different grade, e.g. harder, more resistant or higher qualitythan the core. Such an elastomeric skin, whether or not it is the sameelastomeric material as the core, may be a non-foamed elastomericmaterial, or it may be a foamed elastomeric material having differentcharacteristics, e.g. different void characteristics, to the inner corematerial so as to give the outer skin different properties to the innercore, e.g. so as to make the outer skin more dense, less soft and/ormore resistant to penetration or absorbency than the inner polymer. Forexample a higher number of gas bubbles per unit volume in such a foamedpolymer can result in a softer polymer than a lower number of gasbubbles per unit volume. For example the difference in voidcharacteristics may comprise the skin having a lower number of gasbubbles per unit volume than the core.

Suitable elastomeric materials for use as the core polymer includethermoplastic elastomer (“TPE”) materials, for example compounds basedon styrenic block copolymers such as styrene-ethylene-butadiene-styrene(SEBS) copolymers, e.g. the material Thermolast-K™ (available fromGummiwerk Kraiburg GmbH & Co, Germany), polyblends based on EPDM/PP suchas the material Sarlink™ (available from DSM Thermoplastic ElastomersNL), or polyacrylate/PP blends such as the material Pacrel™ (availablefrom Optatech Corporation, Suomi), thermoplastic polyurethanes such asDesmopan™ (available from Bayer AG, Germany), thermoplastic copolyesterssuch as Hytrel™ (available from Du Pont De Nemours, USA) natural orsynthetic latex type elastomers such as Baystal S™ or Baypren Latex™(available from Polymer Latex, DE), polychloroprenes such as Baypren™(available from Bayer AG, DE), natural rubber and foamed polymers suchas polyurethane foams. Preferably such core polymers are used in afoamed form, e.g. incorporating a dispersion of gas bubbles in theirstructure.

A core of a foamed material such as a foamed elastomeric material may beformed in situ in an injection mould cavity by incorporating into theelastomeric material, such as a known TPE material, a foaming agent,such as the known foaming agents Exocerol AB40E™ or Hydrocerol™,typically at 1-2.5 weight %, typically 2% of the former or 1.5% of thelatter. These foaming agents generate a gas on heating to elevatedtemperatures, typically those used for injection moulding, and if such afoaming agent is included in the elastomeric material, then when it isinjected in a heated state into the mould, the foaming agent will formbubbles within the elastomeric material, resulting in a foam.

Suitable polymers for the outer polymer skin include the above-mentionedelastomeric materials in non-foamed or other grades of foaming e.g.having a lower number of gas bubbles per unit volume than the core. Thismay be achieved by using an elastomeric material without a foamingagent, or with less foaming agent than the core material, or a differentfoaming agent than the core which generates less gas bubbles. Othersuitable polymers for the skin include the above-mentioned elastomericmaterials with different hardness, resistance etc. to the core, andinherently harder polymers different to such elastomers, e.g.polypropylenes, polyamides (such as Nylon™), polyurethanes etc.Preferred polymers for the outer skin are those which bind with the hardplastic material of the toothbrush. For example the polymer for theouter skin may be chemically similar to the hard plastic material of thetoothbrush. A suitable combination of inner and outer polymers is aninner core of a thermoplastic elastomer and an outer skin of the samethermoplastic elastomer in a less soft grade, preferably being athermoplastic elastomer which binds to the hard plastic material.Thermolast-K™ is such an elastomer, and is known for use intwo-component toothbrushes where it is bonded to the hard plasticmaterial of the toothbrush.

Suitably if the inner elastomeric polymer is a relatively soft elastomerand the outer skin is a relatively less soft polymer, e.g. a foamedelastomer core and a non foamed or less foamed elastomer skin, the innercore polymer may have a hardness of ca. Shore A 5 to 30 preferably ca.20-20, and the outer skin may have a hardness of ca. Shore A 65±5. Thethickness of the outer skin may vary from application to application buttypically a thickness of 100 microns to 1.5 mm may be used. It will beappreciated by those skilled in the art that the shape and size of atoothbrush will inevitably impose dimensional constraints, for exampleonly a relatively thin outer skin may be possible in some parts of thetoothbrush where only a relatively thin mass of the elastomeric partsmay be used.

Suitably the elastomeric part(s) of the toothbrush may comprise part(s)of a grip handle in which the elastomer is of sufficient thickness, i.e.from their outer surface to the hard plastic internal skeleton, that theelastomer parts resiliently deform under the pressure of a grippinghand, so that the grip handle has a soft hand feel. For example theelastomer parts of the toothbrush may have a thickness of 3 mm-1.5 cm,e.g. 5 mm-1.0 cm. A suitable grip handle having thick elastomer regionsof this type is known for example from WO 97/29663 the contents of whichare included herein by reference.

The hard plastics material of the other parts of the toothbrush may bemade of any plastics material which is used at present in themanufacture of toothbrushes, particularly in the manufacture of twocomponent toothbrushes which incorporate parts of elastomeric material,and in which the elastomeric parts and plastics parts are bondedtogether. Suitable hard plastics include polypropylenes such asPolypropylenes P 1600™ (Shell) and Apryl 3400 MA1 from Elf Atochem,Novolene 1100 HX™ (BASF), and polyamides such as Ultramil B3™ (BASF).Polypropylenes for example bond readily with Thermolast-K™. Such hardplastics materials typically have a hardness Shire R 80-100.

The hard plastic parts of the toothbrush may be made in a first stage bya conventional process of injection moulding as is common in the art andhas long been used for making toothbrushes. In this first stage the hardplastic part(s) of the toothbrush are made, typically in the form of a“skeleton” or “frame” of the plastics material is made, having one ormore cavities therein corresponding to the intended position(s) anddimensions of the elastomeric material part(s).

The elastomer parts may then be made in a second stage by containing theso plastic material part(s) in a second mould having one or morecavities therein corresponding to the intended position of theelastomeric material part(s), then forming the elastomer part(s) byinjection of the fluid elastomeric material into the one or morecavities. Such a process is for example described in WO 94/05183.Suitable conditions of temperature and pressure etc. for the injectionmoulding process to achieve a bond between the plastic material skeletonand the elastomer material injected into the mould are known in the art,for example as used currently to make two-component toothbrushes.

The elastomer parts of the present invention, having an inner core andan outer skin, may be formed by the known injection moulding process of“sandwich moulding” also called the “skin/core” method, in which theelastomeric material part(s) is/are formed by an injection mouldingprocess in which at least two materials being the materials of the skinand core are injected into a mould cavity simultaneously or successivelyin such a way that the injected polymer is in the form of an inner coreand an outer skin. This process is known from the technical literature.Suitable processes and moulding equipment for such a sandwich mouldingprocess are for example disclosed in U.S. Pat. No. 5,789,033 and U.S.Pat. No. 5,798,069, the contents of which are incorporated herein by wayof reference. In sandwich moulding, a core is introduced into an outerskin component. This process takes place in two or three stages. Firstthe material of the outer skin is injected into the mould cavity topartially fill the cavity with a mass of the material of the outer skin,and then the core component is injected into the mass of introduced skinmaterial to fill and “inflate” the skin material. To finish off, aclosure can be produced with the first, i.e. the skin component near thesprue (the point in the cavity at which the materials are injected).This prevents the core material remaining on the surface and at the sametime cleans the system for the next shot of polymer to be injected intothe mould. U.S. Pat. No. 5,789,033 and U.S. Pat. No. 5,798,069 disclosesandwich moulding processes in which opposed gating injection is used,i.e. the core and skin materials are injected into the mould cavity viarespective separate injection nozzles. Sandwich moulding processes arealso known in which a single nozzle is used to inject both skin and corematerials. Hot runner injection moulding equipment is generallypreferred for the sandwich moulding process.

Suitable injection moulding machinery for sandwich injection moulding isavailable from inter alia Mannesman Demag (Germany). The operatingconditions, e.g. temperature, pressure, flow rate etc. conditions of thesandwich moulding process are preferably selected such that theelastomer part outer skin material bonds to the plastic material of thetoothbrush, “skeleton” or “frame” referred to above. Such conditions canbe determined by practice in the art.

For example in a sandwich moulding process suitable for making thetoothbrush of the present invention a skeleton or frame may be made asdescribed above and this skeleton or frame may be enclosed in a secondmould having cavities therein corresponding to the intended position ofthe elastomer parts, then the skin material, e.g. a material such asthose described above, for example an elastomeric material, may beinjected into the cavity, typically in an amount comprising ca 20-30% ofthe total cavity volume. Then the core material, e.g. a material such asthose described above, for example an elastomeric material, e.g. thesame elastomeric material as the skin material and containing a foamingagent may be injected into the cavity to form the core, and the corematerial fills and inflates the skin. Suitably if the core materialincludes a foaming agent expansion of the core material within the mouldmay occur as a result of the temperature of the mould. If the corematerial is a foaming elastomer, e.g. includes a foaming agent, then aquantity of such a core material may be injected into the cavity suchthat the combined volume of skin and core materials fills ca. 50-70%,e.g 60% of the cavity, and the expansion of the core material as foamingoccurs may then cause sufficient expansion that the core and skinmaterials fill the cavity.

Alternatively the elastomer parts of the present invention, having aninner core and an outer skin, may be formed by an injection mouldingprocess that employs internal foaming of an injected elastomer materialto generate both skin and core. For example an elastomer material suchas those described above may have incorporated into it a foaming agent,such as those described above. These foaming agents generate a gas onheating to elevated temperatures, typically those used for injectionmoulding, and if such a foaming agent is included in the elastomericmaterial, then when it is injected in a heated state into the mould, thefoaming agent will form bubbles within the elastomeric material,resulting in a foam. However an injection mould for a toothbrush isnormally made of a heat conducting metal and will normal include coolingfluid channels in its metal mould blocks to rapidly cool the toothbrushformed therein. Consequently the outer parts of the moulded elastomerbeing in contact with the metal mould cavity surfaces can be arranged tocool more rapidly so as to foam less, resulting in an outer skin in anon foamed state or in a less foamed state than the inner core parts ofthe material further away from the metal walls of the mould cavity.

Accordingly this invention further provides an injection mouldingprocess for making a toothbrush comprising hard plastic and elastomericmaterial parts, in which a hard plastic material “skeleton” or “frame”is provided having one or more cavities therein corresponding to theintended position of the elastomeric part(s), this skeleton or frame islocated within a mould having one or more cavities corresponding to theintended position of the elastomeric parts, and the elastomeric part(s)are formed within the said mould cavities by an injection process whichforms an inner core of a soft elastomeric material wholly or partlyenclosed within an outer skin of a second polymer material. Theinjection process is preferably a sandwich moulding or foaming process.

The invention further provides a mould suitable for use in such aninjection moulding process, having cavities therein corresponding to theintended position of the elastomeric parts, and provided with means tocarry out a sandwich moulding process therein. The mould is suitablyprovided with injection ports to facilitate a sandwich moulding process.The invention further provides a mould suitable for use in such aninjection moulding process, having cavities therein corresponding to theintended position of the elastomeric parts, suitable for injecting anelastomeric material which includes an internal foaming agent therein.

The invention will now be described by way of example only, referringto:

FIG. 1 which shows a toothbrush according to this invention.

FIG. 2 which shows an enlarged cross section through part of thetoothbrush of FIG. 1.

FIG. 3 which shows an enlarged cross section through an alternativeconstruction of part of the toothbrush of FIG. 1.

FIG. 4 which shows the sandwich moulding process used for making atoothbrush of FIG. 1.

Referring to FIG. 1 a toothbrush is shown in longitudinal section,comprising a handle 1, a head 2 on which are mounted bristles 3, and aneck region 4 between the handle 1 and head 2. The toothbrush of FIG. 1is made partly of a hard polypropylene material, which is in the form ofa frame 5 having cavities 6 therein, and partly of parts 7, 8, 9, 10,11, 12 which comprise an elastomeric material. The cavities 6 are inpositions which correspond to the positions of the elastomeric materialparts 7-12.

Part 7 is a grip pad on the handle 1. Part 8 is a flexible link betweenthe handle 1 and neck 4 of the toothbrush comprising an aperture in thehard plastic material which is occupied by the elastomeric material.Part 9 is a flexible link in the toothbrush neck 4, part 10 is aflexible link between the head 2 and neck 4 of the toothbrush 2comprising apertures in the hard plastic material of the neck which areoccupied by the elastomeric material. Parts 11 are flexible links in thehead 2 of the toothbrush, each comprising a widthways extending groovebeing occupied by the elastomeric material. Part 12 is a soft bufferaround the head 2, comprising a projecting rim around the head 2.

Each of parts 7-12 comprises an elastomeric core made of a softthermoplastic elastomeric material of hardness Shore A ca 5; and anouter enclosing skin of a less soft grade of the same thermoplasticelastomeric material. Two alternative structures of the elastomericmaterial parts 7-12 are shown in FIGS. 2 and 3.

Referring to FIG. 2, a cross section through the part 7 of thetoothbrush of FIG. 1 which is circled in FIG. 1 is shown, althoughsections through other elastomeric parts shown in FIG. 1 would beidentical. FIG. 2 shows part 21 of the plastic material of thetoothbrush. The elastomeric material part 22 comprises a core 23 of afirst soft elastomeric material polymer material and an outer skin 24 ofa second polymer. The second polymer of the outer skin 24 is a flexiblepolymer which is harder and less permeable than the elastomeric materialof the core. At the interface 25 between the elastomeric material part22 and the plastic material 21 the outer polymer skin 24 is bonded tothe plastic material 21. The elastomeric material parts 7-12 are formedby a process of sandwich moulding.

Referring to FIG. 3, a cross section through the part 7 of thetoothbrush of FIG. 1 which is circled in FIG. 1 is shown, althoughsections through other elastomeric parts shown in FIG. 1 would beidentical. FIG. 3 shows part 31 of the plastic material of thetoothbrush. The elastomeric material part 32 is a soft foamedthermoplastic elastomeric material, i.e. within which there are numerousinternal bubbles 33. As is shown in FIG. 3 the extent of foamingdecreases towards the outer surface 34 of the elastomeric material part32, and the part 35 of the elastomeric material part 32 immediatelyadjacent to the outer surface 34 is essentially non-foamed. Consequentlythe outer parts 35 of the polymer layer are less soft than the innercore part closer to the plastic parts 31. At the interface 36 betweenthe elastomeric material part 32 and the hard plastic material part 31these parts are bonded together.

The elastomeric material part 32 has been formed by positioning the hardplastic parts 31 in the cavity of a injection mould (not shown), andinjecting an elastomeric material which includes a foaming agent intothe cavity under known conditions such that the elastomeric material andplastic parts bond. At the temperature of the mould the foaming agentgenerates gas bubbles 33, but the metal walls of the mould (not shown)are a good heat conductor and the outer layers 35 of the injectedelastomeric material rapidly cool down immediately after the elastomericmaterial is injected in so that less foaming occurs in these layers. Theplastic material part 31 is not as good a heat conductor as the metalinjection mould (not shown) in which the elastomeric material part 32has been formed, consequently bubbles 33 are formed in the parts of theelastomeric material 32 adjacent to the plastic parts 31.

The thickness of the elastomeric material part, e.g. the distance fromthe outer surface 34 to the plastic part 31 may be typically 3 mm-1.5cm.

Referring to FIG. 4A, part of an injection mould 40 is shown overall,being a two part mould having two halves 41, 42 with a split line A-A,and defining a mould cavity 43 between the two halves 41, 42. There isan injection gate 44, of a known type suitable for sandwich moulding.The mould 40 encloses a hard plastic part 45 of a toothbrush handlewhich has previously been made in a separate first stage injectionmoulding process. The part 45 shown is part of the grip handle of thetoothbrush, wth a neck 46 extending therefrom, but the head is notshown. Part of the cavity 43 is also defined by a cavity in the handlepart 45.

Referring to FIG. 4B a first material 47 has been injected into thecavity 43 via gate 44. The material 47 is a thermoplastic elastomer suchas Thermolast-K™, and the quantity injected is sufficient to fill ca.20-30% of the cavity 43. The moulding conditions are such that the thematerial 47 is injected in a hot fluid state, but cools slightly in thecavity 43 to increase its viscosity.

Referring to FIG. 4C, a second material 48 has been injected into thecavity 43, in a way such that the material 48 flows into the centre ofthe mass of first material 47, to inflate the mass of material 47 sothat the material 47 surrounds the inner core of material 47. The secondmaterial 48 is typically a thermoplastic elastomer such as Thermolast-K™but including a foaming agent such as Exocerol AB40E™ or Hydrocerol™,typically at 1-2.5 weight %, typically 2% of the former or 1.5% of thelatter. The quantity of second material 48 injected is such that thecombined first and second material 47, 48 occupy ca. 60% of the cavity43. The second material 48 is of a lower viscosity than the firstmaterial 47 in the cavity 43.

Referring to FIG. 4D, the second material 48 has foamed under the hotconditions inside the cavity 43, and the second material 48 hasconsequently expanded within the skin of first material 47 so that themass of combined first and second material fills cavity 43. The smallresidual hole (not shown) in the skin 47 where the second material haspenetrated into the core of first material 47 has been closed by a smallinjection of first material 47 through gate 44.

The conditions inside the cavity 43 are such that the first material 47bonds to the plastic material part 45. Suitable conditions to achievebonding are known in the art, e.g in conventional toothbrushmanufacturing processes.

In FIG. 4 the sandwich moulding process shown uses a single gate 44, butit will be understood that further gates (not shown) may be provided toinject first and second materials into other parts of the toothbrush. Itwill also be appreciated that the process shown in FIG. 4 may be adaptedfor use with opposed gate techniques, although id materials 47, 48 areinjected from sides of the cavity 43 on opposite sides of the handle 45,it will be necessary to provide some communication channels eitherthrough or around the part 45 to enable the core to be injected. In themanner described.

1-36. (canceled)
 37. A toothbrush comprising a handle, a head on whichare mounted bristles, with optionally a neck region between the head andhandle, the toothbrush being made partly of a hard plastic material andhaving at least one part made of an elastomeric material, wherein; atleast part of the at least one elastomeric material part comprises aninner core of an elastomeric material wholly or partly enclosed withinan outer flexible skin of the same elastomeric material comprising thesame monomer units as the core but having different physicalcharacteristics to the inner core material when made by a process inwhich: a hard plastic part of the toothbrush is made in a first stage bya process of injection moulding in the form of a skeleton of the hardplastic material having one or more cavity therein corresponding to theintended position(s) and dimensions of the elastomeric material part(s),then; this skeleton is enclosed in a mould having at least one cavitytherein corresponding to the intended position of an elastomer part,then the skin material is injected into the cavity, then the corematerial is injected into the cavity to form the core and to fill andinflate the skin.
 38. A toothbrush according to claim 37 wherein thecore comprises a foamed elastomeric material and the skin comprises thesame elastomeric material in a non-foamed state.
 39. A toothbrushaccording to claim 37 wherein the core comprises a foamed elastomericmaterial and the skin comprises the same elastomeric material in afoamed state having different void characteristics to the inner corematerial.
 40. A toothbrush according to claim 39 wherein the skincomprises the same elastomeric material in a foamed state having a lowernumber of gas bubbles per unit volume than the core.
 41. A toothbrushaccording to claim 37 wherein the elastomeric material of the corecomprises a foamed elastomeric material having a hardness of Shore A 5to 30, and the outer skin comprises a non foamed elastomeric material oran elastomeric material less foamed than the material of the core havinga hardness of Shore A 65±5, the thickness of the outer skin being in therange 100 microns-1.5 mm.
 42. A toothbrush according to claim 41 whereinthe elastomer part of the toothbrush has a thickness of 3 mm-1.5 cm. 43.A toothbrush according to claim 37 wherein the elastomeric material ofthe core and skin is selected from the group of compounds based onstyrenic block copolymers such as styrene-ethylene-butadiene-styrene(SEBS) copolymers, polyblends based on EPDM/PP, polyacrylate/PP blends,thermoplastic polyurethanes, thermoplastic copolyesters, natural orsynthetic latex type elastomers, polychloroprenes, natural rubber andpolyurethane foams.
 44. A toothbrush according to claim 37 wherein theskin material is injected into the mould cavity in an amount comprising20-30% of the total cavity volume then the core material is injectedinto the cavity to form the core and to fill and inflate the skin.
 45. Atoothbrush according to claim 37 wherein the core comprises an elastomermaterial which includes a foaming agent and the quantity of such corematerial injected into the cavity is such that the combined volume ofskin and core materials fills ca. 50-70% of the cavity and the expansionof the core material as foaming occurs then causes sufficient expansionthat the core and skin materials fill the cavity.
 46. A toothbrushaccording to claim 37 when made in a process in which: a hard plasticpart of the toothbrush is made in a first stage by a process ofinjection moulding in the form of a skeleton of the hard plasticmaterial having one or more cavity therein corresponding to the intendedposition(s) and dimensions of the elastomeric material part(s), then;this skeleton is enclosed in a mould having at least one cavity therein,bounded by a wall, corresponding to the intended position of anelastomer part, then an elastomer material having incorporated therein afoaming agent is injected into the mould and outer parts of theelastomer material injected into the mould are arranged to cool morerapidly so as to foam less to result in an outer skin in a non foamedstate or in a less foamed state than the inner core parts of thematerial further away from the walls of the mould cavity.